Nanoarchitectonics of highly dispersed polythiophene on paper for accurate quantitative detection of metal ions

π-Conjugated polymers such as polythiophene provide intramolecular wire effects upon analyte capture, which contribute to sensitive detection in chemical sensing. However, inherent aggregation-induced quenching causes difficulty in fluorescent chemical sensing in the solid state. Herein, we propose a solid-state fluorescent chemosensor array device made of a paper substrate (PCSAD) for the qualitative and quantitative detection of metal ions. A polythiophene derivative modified by dipicolylamine moieties (1poly), which shows optical changes upon the addition of target metal ions (i.e., Cu2+, Cd2+, Ni2+, Co2+, Pb2+, Zn2+, and Hg2+), was highly dispersed on the paper substrate using office apparatus. In this regard, morphological observation of the PCSAD after printing of 1poly suggested the contribution of the fiber structures of the paper substrate to the homogeneous dispersion of 1poly ink to suppress aggregation-induced quenching. The optical changes in the PCSAD upon the addition of metal ions was rapidly recorded using a smartphone, which was further applied to imaging analysis and pattern recognition techniques for high-throughput sensing. Indeed, the printed PCSAD embedded with 1poly achieved the accurate detection of metal ions at ppm levels contained in river water. The limit of detection of the PCSAD-based sensing system using a smartphone (48 ppb for Cu2+ ions) is comparable to that of a solution-based sensing system using a stationary spectrophotometer (16 ppb for Cu2+ ions). Therefore, the methodology based on a combination of a paper-based sensor array and a π-conjugated polymer will be a promising approach for solid-state fluorescent chemosensors.


Synthesis of 1 poly
The polythiophene derivative (1 poly ) was obtained by oxidative polymerization of a dpa-attached thiophene monomer (1) with FeCl 3 .S1 Monomer 2 was synthesized according to a previous report, S2 for obtaining 1 by the introduction of 2,2'-dipicolylamine into 2.A methyl group-substituted thiophene monomer at 4-position was employed to avoid the generation of byproducts (α-β' coupling) in the polymerization process.S3,S4 The polymerization method was selected from the viewpoint of reactivity to heterocyclic amine-attached thiophene monomers and the yield of homopolymers.S5,S6 The polymerization was carried out after substituting the dpa unit into the thiophene ring to avoid the formation of heterogeneous copolymers of 2 and unreacted starting material (1).In addition, thermal extraction was performed with a mixture of methanol and hydrazine monohydrate to remove Fe ions from the obtained product.NMR analysis result of 1 poly indicated that regioselective product with headto-tail orientation with high yields (80-90%).S1,S6 Scheme S1 Synthesis of the dpa-attached PT (1 poly ).(a) 2,2'-Dipicolylamine, K 2 CO 3 , CH 3 CN, reflux, (b) FeCl 3 , dry CHCl 3 , r. t.These materials, 1, 2, and 1 poly were obtained according to a previously reported protocol.S1

Static quenching constants
With an increase in quencher concentrations (i.e., metal ions), the decrease in fluorescence emission intensity of the fluorophore (1 poly ) corresponds to the quencher concentrations as described by the Stern-Volmer relationship (eq.1); S7 where I 0 and I are the fluorescence emission intensity in the absence and the presence of a quencher metal ion, K SV is the Stern-Volmer quenching constant (for dynamic quenching), K S is the static quenching constant, and [Q] is the concentration of the quencher metal ions.Since K S is more dominant than K SV in the case of polymer-based fluorescent materials in aqueous buffer solutions, the dynamic quenching is ignorable.S8 Hg 2+ 7.0 × 10 3 a) N.D.: not determined owing to no contribution as the quencher metal ion.9. Semi-quantitative assay using LDA Fig. S19 Semi-quantitative assay against Cu 2+ , Ni 2+ , and Co 2+ ions.Each measurement was repeated 16 times.

Fig. S20
The canonical score plot of the semi-quantitative assay.
Table S3 The jackknifed classification matrix of the semi-quantitative assay for Co 2+ , Ni 2+ , and Cu 2+ ions 10.Real-sample analysis using SVM Table S4 The spiked and recovery test using the PCSAD for metal ions in the river water sample

Fig. S14
Fig. S14The fluorescence intensity of the printed 1 Poly on the 384 wells before (15% at 25 °C) and after exposure to high humidity (95% at 25 °C).

Fig. S18
Fig. S18The canonical score plot of the qualitative assay.

Fig. S21
Fig. S21 Regression analysis using SVM for the Cu 2+ ions in the commercial artificial seawater sample.

Table S2
The jackknifed classification matrix of the qualitative assay for 6 metal ions

Table S5
The elements of the original river water sample

Table S6 .
The spiked and recovery test for the Cu 2+ ions in the commercial artificial seawater sample

Table S7 .
The ingredient list of the commercial artificial seawater sample